1. Field of the Invention
This invention relates to organic plastics and, more particularly, to organic plastic systems containing an additive capable of reducing or eliminating the curing shrinkage.
2. Description of the Prior Art
Curing shrinkage in organic plastics, and particularly in exothermic plastics, is well known. For certain applications, such as in casting and molding, the shrinkage adversely affects the quality of the final product. In fact, the shrinkage effect is a constant problem for the plastic application engineers for precision casting and molding. To overcome the shrinkage, engineers have tried to mix various plastic materials with diversified shrinkage and expansion properties or to use elaborate precautions and adjustments to compensate the shrinkage so as to obtain a final cast that fits the specification. Mixing plastic materials to compensate shrinkage generally is achieved only at the sacrifice of other desirable properties. Adjustment of molds for the shrinkage generally fails to provide the precision and the desired surface properties in the resultant cast.
The use of various organic blowing agents to produce flexible and rigid plastic foams are also well known. The use of this type of agent for controlling shrinkage, however, is not desirable because blowing action is difficult to control and, more particularly, the resultant products usually have weakened structural properties and are not desirable for many applications.